Specialized Sertoli cell functions such as the synthesis of transferrin are modulated as a result of association with different stages of he cycle of the seminiferous epithelium. The cycle is defined by the germinal cell composition of the tubules and thus it is possible that the germinal cells modulate Sertoli cell functions. Preliminary results have shown that germinal cells can stimulate transferrin mRNA synthesis in Sertoli cells in culture and in vivo. There is evidence that germinal cells secrete a protein which can stimulate the synthesis of specialized secretion products from Sertoli cells. The goal of this proposal is the purification and characterization of this protein designated Cycle Regulatory Protein (CRP). Small amount of CRP will be purified by chromatography using HPLC and subjected to sequence analysis by gas-phase protein sequencing. The information from the amino acid sequence will be used to construct oligonucleotide probes which will be used to screen a cDNA library for a clone containing a CRP cDNA. Information from the cDNA sequence will be used to synthesize peptides corresponding to hydrophilic regions of the CRP. These peptides will be used to generate polyclonal antibodies to the CRP which in addition to the cDNA will be used to probe the cellular sites of origin and action of the CRP. Antiserum will be used in immunoprecipitation and immunohistochemical studies while the cDNA will be used in Northern blots and in situ hybridization. Results from these studies will be very important in clarifying the interaction of germinal cells and Sertoli cells in the process of spermatogenesis. A more thorough understanding of spermatogenesis has significant impact on problems of male fertility and contraception.